Communicating information through light instead of electrical signals has many useful applications. The medium for light travel is typically a fiber optic cable. A transceiver circuit is typically coupled to each end of the fiber optic cable and includes an optical transmitter that performs transmission functions and an optical receiver that performs receiving functions. The transmitter includes a laser that acts as a source of light. An important component in the transceiver is an optical element that receives the light generated by the laser and launches the light into the fiber optic cable in a manner that minimizes reflections back to the laser and that provides favorable launch conditions to increase the bandwidth of the system. There are some situations in which it is desired to decrease the optical power of the laser signal.
There are several current prior art approaches to decrease the optical power of the laser signal. One approach to decrease the optical power of the laser signal is to apply partially reflective coatings on a surface of the optical element. Although these coatings provide tolerable control over the direction in which unwanted light is reflected, these coatings tend to be expensive. Furthermore, these coatings are prone to de-adhesion from the optical element, which can lead to undesirable results in the field.
Another approach to decrease the optical power of the laser signal is to machine or otherwise cause one surface of the optical element to become a textured surface. For example, surfaces of the optical element can be roughened surfaces. These textured surfaces act to scatter incoming light by re-distributing the light in a wide range of directions. It is noted that these textured surfaces do not absorb the incoming light. Unfortunately, the scattered light may cause interference or other problems with components adjacent to the optical element.
Yet another approach to utilize diffractive optical elements and partial beam blockers in the optical signal path between the laser and the fiber optic cable. Unfortunately, the diffractive optical elements and partial beam blockers tend to influence the optical signal's modal behavior. Consequently, these elements tend to complicate the design and placement of the laser, especially in terms of determining the appropriate launch intensity.
Based on the foregoing, there remains a need for a method and apparatus that controls the attenuation of an optical element that overcomes the disadvantages set forth previously.